On 07/11/2011 01:08 PM, JB wrote: > Michal Schmidt<mschmidt<at> redhat.com> writes: >> First, sub-service-1.service and sub-service-2.service will be started >> in parallel. When they're running, main-service-1.service will be >> started by processing its ExecStart* commands sequentially. >> ... > > OK. > Q: The sub-service-1.service and sub-service-2.service will be run as stand- > alone processes (of whatever kind they are: daemon, master/slave, > multithreaded), Yes. > with no back references or dependecies of any kind > (parent-child like, shared resources, etc) to main-service-1.service ? There is no parent-child relationship between services. The parent of all services is systemd (PID 1). Services do not spawn other services directly. Only systemd spawns services. About "dependencies of any kind": In the example there are requirement and ordering dependencies between main-service-1.service and the sub-services (that's what Requires= and After= directives specify). systemd maintains the graph of these dependencies in its data structures. > 2. > main-service-2.service: > [Unit] > Description=Main service 2 > After= ... > ... > [Service] > Type=forking<---------------------- any other type too ? > ExecStartPre= exec /etc/init.d/sub-service-1 > ExecStartPre= exec /etc/init.d/sub-service-2 > ExecStart= /usr/sbin/some-service > ExecStartPost= > ExecStartPost= > ... > > Would the above be correct setup-wise ? Synchronous starting of other services may lead to deadlocks in some cases (e.g. https://bugzilla.redhat.com/show_bug.cgi?id=690177). But even if you avoid the deadlock, this unit file is still horrible. Using systemd's dependency mechanisms (Requires, Wants, After, ...) is definitely cleaner. > Are there any restrictions on those Pre (and Post) commands ? One limitation was already mentioned somewhere in this thread - these commands must not fork off daemons. >> Parallelism in systemd happens between multiple units, but never between >> ExecStart* commands of one unit. >> Requesting parallelism within one unit seems like over-engineering to >> me. You can always split your unit to smaller ones if you want >> parallelism. > > But this is what Steve, I believe, wants to do with nfs (to have a bunch of > services started from the main one, as under current SysV init system, so his > users are not confused by the startup of all these individual service files). I proposed a way to do this cleanly using systemd targets elsewhere in this discussion. >> Take a look at 'systemd-analyze plot' where you can clearly see >> services starting in parallel. > > Well, I wish I could (I am on F15) ... > > $ systemd-analyze plot > <?xml version="1.0" encoding="UTF-8"?> [...] Store it to an SVG file and then view it. Michal -- devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxxx https://admin.fedoraproject.org/mailman/listinfo/devel
